It has long been a common practice in the well art to suspend an inner pipe, typically a casing string, concentrically within an outer member, typically an outer casing string or a wellhead member, by means of a hanger comprising a hanger member connected to the inner pipe and having a downwardly directed shoulder which engages an upwardly directed shoulder on the outer member as the inner pipe is run in. As the art developed, it became necessary to minimize the annular space between the inner and outer hanger members, and prior art workers have developed hangers employing a retractable hanger device carried by a mandrel on the inner pipe and capable of expanding into engagement with an outer hanger member when, as the inner pipe is run in, the mandrel reaches the outer hanger member. Pipe hangers of this type have become particularly important with the advent of offshore practices in which the hanger is located at the mudline and the outer pipe above the wellhead is of the same diameter as the outer casing below the wellhead and the annular space available for the hanger is relatively small. Such hangers are disclosed, for example, in the following U.S. patents:
U.S. Pat. No. 3,420,308; Putch
U.S. Pat. No. 3,472,530; Fowler
U.S. Pat. No. 3,741,589; Herd et al
U.S. Pat. No. 3,893,717; Nelson
Though hangers of this general type have achieved considerable success, they still present problems which increase in severity as the annular space available at the hanger decreases and the weight of the pipe string to be supported increases. Thus, it has been difficult to assure that the retractable hanger device, which must retract radially as the mandrel passes into the outer hanger member, will expand into proper engagement with the outer hanger member. Further, with the outer hanger member provided with grooves to accommodate the retractable hanger device, engagement between the outer member and the retractable device has not been adequate to assure that the large tension loads applied by the inner pipe string are adequately supported. Both problem areas tend to require structures which are unduly large in radial directions, unduly complex and excessively expensive.